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For NPR and WBUR Boston, I'm Jeremy Hobson. It's HERE AND NOW. Scientists along the East Coast are alarmed and puzzled by what's been washing up this summer on the beaches from Virginia to New York - dead bottlenose dolphins, at least, 91 in July alone. Compare that to just nine last year and 16 the year before. There is no word yet on what's causing the increase. It appears that four had been sick with pneumonia, and one died of morbillivirus, which killed hundreds of dolphins along the East Coast in the 1980s. Jenn Dittmar is the stranding coordinator with the National Aquarium in Baltimore, and she is with us now. Jenn, welcome.

JENN DITTMAR: Thank you so much for having me.

HOBSON: Well, tell us what you make of these dead dolphins washing up along the East Coast.

DITTMAR: There are some preliminary talks that it's possible that it could be an event similar to the 1987/1988 event where there were almost 750 bottlenose dolphins that had washed up along the East Coast due to a measles-like virus. And they're testing for a lot of other things, such as some potential bacterias or possibly biotoxins and different viruses. But it is definitely alarming, knowing what's going on out there.

HOBSON: If it is this morbillivirus that killed dolphins back in 1987, would that be a relief for you, or would that be the worst-case scenario?

DITTMAR: It's kind of a double-edge sword. It would mean that the event would likely continue longer because that event, you know, continued almost over a two-year period. And basically, what happens in a case like that is you get animals that don't have an immunity to something like a morbillivirus that if they become infected will obviously succumb to symptoms from that. Whereas if they're exposed to something like morbilli over a period of time, there will be individuals that can develop an immunity to it where at one point the, you know, the deaths will start to kind of decrease. So it's hard to tell where we fall if it happens to be something like that in an event like this and how it will really affect the overall population.

HOBSON: And if it is not this morbillivirus, what would be the next thing that you would be looking for that it could be that's causing these deaths?

DITTMAR: The dolphins that have stranded have not had any sort of consistent external signs that might suggest it's like entanglement and fishing gear or boat-strike injuries. So that may lead us to believe that something such as biotoxins or maybe some sort of bacterial disease or another type of viral disease.

HOBSON: Tell us about the bottlenose dolphin that's being affected in this case. What are bottlenose dolphins compared to other dolphins?

DITTMAR: Bottlenose dolphins are a certain species. They're kind of the iconic dolphin that people think of when they go to the beach and see dolphins. Their genus and species is Tursiops truncates, and there's evidence to suggest that that single species actually has two different populations. So there's what we call a coastal migratory stock, which is a stock that you would usually see if you're at the beach in New Jersey or Virginia and see dolphins. So that's one stock of this species, but there's also evidence that strongly suggests that there's an offshore stock as well that tends to stay much further offshore.

They don't come in close to the coast where the other stock does, and there are physical differences that offshore stock is much usually darker in color, and they're usually much longer and more robust animals. And you would expect that if they're offshore traveling further distances and having to, you know, work harder for their food.

HOBSON: Jenn Dittmar is the stranding coordinator with the National Aquarium in Baltimore talking with us about the deaths of dozens of dolphins this year, much higher number than in previous years. Jenn, thank you so much.

DITTMAR: No problem. Thank you.

HOBSON: And still to come, that amber alert for two Southern California children now extends up into the Pacific Northwest. We'll hear about that after a break. HERE AND NOW. Transcript provided by NPR, Copyright NPR.